Thermostatic switch



United States Patent THERMOSTATIC SWITCH Arthur J. Kercher, Berkeley,Calif., assignor of one-half to William Wesley Hicks, San Francisco,Calif.

Application May 11, 1956, Serial No. 584,395

4 Claims. (Cl. 200-138) This invention relates generally to thermostaticswitches and more particularly to thermostatic switches of the typeutilized for controlling line voltage circuits.

In many heating applications it is desirable to control the heatingequipment by a thermostatic switch connected directly in the powerlines. The thermostats adapted for such service require heavierconstruction and heavier electrical contacts which increases the masswhich must be moved when the switch is opened and closed. In addition,in such switches contact pressure must remain positive up until themoment the switch is opened to prevent excessive arcing. Suchthermostatic switches have been provided with a snap action to makepossible a quick make and break in order to prolong the life of thecontacts and to prevent radio interference. However, it has been foundthat in utilizing a snap action the movable contacts have a tendency tovibrate and bounce off of the stationary contacts when the switch ismoved into a closed position. This causes excessive arcing whichshortens the life of the contacts. In addition, it has been found thatsuch snap action switches are relatively insensitive'and acterratically.

In general, it is an object of the present invention to provide animproved thermostatic switch of the above character which ischaracterized by its reliability and long life.

Another object of the invention is to provide a thermostatic switch ofthe above character which has greater sensitivity.

A further object of the invention is to provide a switch of the abovecharacter in which the movable contacts do not vibrate or bounce off ofthe stationary contacts when the switch is moved to a closed position.

A still further object of the invention is to provide a switch of theabove character in which arcing of the contacts is reduced when theswitch is moved to a closed position.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment has been setforth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure 1 is a front elevationl view of a thermostatic switch embodyingthe present invention showing both sets of contacts in an open position.

Figure 2 is a front elevational view similar to that shown in Figure 1showing one set of contacts in an open position and one set of contactsin a closed position.

Figure 3 is a front elevational view similar to Figures 1 and 2 butshowing both sets of contacts in a closed position.

Figure 4 is a cross sectional view taken along the line 4-4 of Figure 2.

Figure 5 is a cross sectional view taken along the line 5-5 of Figure 2.

In general, the present invention consists of a thermostatic switch inwhich the movable contact is positively loaded in one direction byspring means to prevent vibration and rebound and to prevent the movablecontact from hanging up on dead center.

As shown in the drawing, my improved thermostatic switch consistsgenerally of a mounting 11 which carries electrical contacts andoperating parts. In the structure illustrated, the mounting consists ofa metal mounting member 12 carrying a pair of spaced posts 13. Asdescribed in my Patent No. 2,713,100 a pair of spirally wound bimetallicstrips 14 have one of their ends attached to the posts 13 and have theother of their ends engaging and carrying a contact arm 16. Temperaturechanges cause the bimetallic strips 14 to swing the free end of contactarm 16 between two positions.

In order to afford adjustment for the switch so that the bimetallicelements 14 will operate the contact arm 16 at different temperatures,adjustment means 18 operable by the knob 19 is provided and is identicalto that disclosed in my Patent No. 2,713,100. As also described in myPatent No. 2,713,100 the contact arm 16 is adapted to be engaged andoperated by a lever 21 which is manually controlled by the knob 19 for apurpose hereinafter described.

A movable contact member 24 is loosely mounted on one side of the freeend of contact arm 16 by suitable means such as rivet pins 26. The rivetpins 26 serve to prevent rotation of the contact member 24 relative tothe arm 16, but permit limited pivotal or swinging movement between thecontact member and the arm 16 about an axis at right angles to the axesof the rivet pins 26.

A U-shaped mounting block 28 of suitable insulating material is mountedon the mounting member 12. A pair of substantially U-shaped metal bars29 are spaced apart and are fixed to the leg 31 of the mounting block 28by rivets 32. A pair of stationary contacts 33 are mounted on the freeends of the bars 29 and are adapted to be engaged by the contact member24 as shown in Figure 4.

A pair of substantially U-shaped bars 36 are also fixed to the leg 37 ofthe mounting block 28 by suitable means such as rivets 38. A stationarycontact 39 is mounted on the lowermost bar 36 and is adapted to beengaged by a movable contact 41 mounted on one leg 42 of a springlikemember 43. The spring-like member 43 is provided with another leg 44which is offset slightly from leg 42 and is secured to the uppermost bar36 by suitable means such as rivets 46.

Suitable means is provided for operating the movable contact 41 from thecontact arm 16 and can consist of a projection 49 which is mounted onthe free end of the contact arm 16 on the side opposite the side onwhich the contact member 24 is mounted. The projection 49 is adapted toengage a portion 51 on the leg 42 so that upon movement of the contactarm 16 to the right, as viewed in Figure 1, the leg 42 will also bemoved to the right to open contacts 41 and 39 for a purpose hereinafterdescribed.

Suitable means is also provided for biasing or positively loading thecontact arm 16 in one direction to prevent vibration or rebound uponmovement of contact member 24 into engagement with stationary contacts33 and to prevent the contact member from hanging up in dead center.Such means can consist of a small coil spring 53 housed within a recess54 in the projection 49. As can be seen from Figure 5, one end of thespring engages the bottom of the recess 54 and the other end of thespring engages the portion 51 on the leg 42 to continuously urge thecontact arm 16 in a direction away from the leg 42.

Operation of my thermostatic switch can now be described as follows: Letit be assumed that the thermostatic switch is in the position shown inFigure 1. As shown, contacts 39 and 41 have been locked in an openposition by the lever 21 which has moved the free end of the contact arm16 to the right as viewed in Figure 1. The projection 49 on the contactarm has moved the leg 42 to the right and has opened contacts 39 and 41.

When the contact arm 16 is held in the position shown in Figure 1 by thelever 21, the contact arm is unresponsive to the bimetallic elements 14because the lever 21 serves to lock the contact arm in the extreme rightposition. In this position the switch is in a position which is termedthe off position, that is, both sets of contacts are open.

When it is desired to move the thermostatic switch from the offposition, the knob 19 is rotated in a clockwise direction, as viewed inFigures 1 and 2. Assuming that the thermostatic switch is connected to aheater, the knob 19 is rotated to a position determined by thetemperature which it is desired for the switch to operate to turn offthe heater, as, for example, 70 F.

Upon rotation of the knob 19 from the off position shown in Figure 1,the lever 21 is moved to the left as viewed in Figure 2, and the contactarm 16 is freed. As soon as the contact arm 16 is freed by the lever 21,the free end of the contact arm 16 is moved to the left, as viewed inFigure 2, by the spring-like member 43, and the contacts 39 and 41 areclosed.

Assuming that the temperature is above 7 F., the contact member 24 isnot moved into engagement with stationary contacts 33 by the bimetallicelements 14. The spring 53 continuously urges the free end of thecontact arm 16 away from the spring-like member 43, but its force isinsufficient to cause an appreciable movement of the contact arm 16independently of the bimetallic ele ments 14.

Now let it be assumed that the temperature drops below 70 to causeoperation of the contact arm 16, and movement of the contact member 24into engagement with the stationary contacts 33, as shown in Figure 3.It has been found that the snap action of the contact arm 16 in closingcontacts 24 and 33 causes vibration and rebound of the contact arm 16and the contact member 24 which causes excessive arcing and damage tothe contacts. The impact in closing the contacts actually causes aslight rebound of the contacts and vibration in thecontact arm 16 andcontacts which hampers or inhibits a proper closure between the contactmember 24 and the contacts 33.

The use of the spring 53 greatly reduces or eliminates this rebound orvibration and therefore reduces the arcing during closing of contacts 24and 33 and therefore greatly increases the life of the contacts. snubberand is positioned so that it is adjacent the free end of the contact arm16 and adjacent contact member 24 to be most effective. The coil spring53 serves to positively load or bias the contact arm 16 in one directiontoward a position in which contacts 24 and 33 are closed.

The spring 53 acts as a I Thus, the force required to move the contactmember 24 into engagement with the contacts 33 is less than required toopen the contacts 24 and 33.

Since the coil spring 53 is compressed more in a closed position of themovable contacts than in an open position, there is a difierential inforces which improves the sensitivity of the thermostatic switch and thereliability of the thermostatic switch because it prevents the contactarm 16 from hanging up on dead center.

It is apparent from the foregoing that 'I have provided an improvedthermostatic switch having greater sensitivity and reliability and inwhich contact life is greatly increased.

I claim:

1. In a switch, a stationary contact, a movable contact, a contact arm,said movable contact being mounted on one end of saidcontact'arm, meansengaging the other end of said arm for moving the arm and the movablecontact between open and closed positions relative to said stationarycontact, and means engaging said arm for continuously urging said armand movable contact towards one of said positions.

2. A switch as in claim 1 wherein said last named means includes aspring.

3. In a thermostatic switch, a contact arm, a movable contact mounted onone end of said contact arm, a stationary contact, temperatureresponsive means engaging the other end of said arm for moving saidcontact arm and said movable contact between open and closed posi tionsrelative to said stationary contact, and spring means engaging said armfor continuously urging said arm and said movable contact to a closedposition, said spring means being mounted on the side of said armopposite the side on which said movable contact is mounted and adjacentthe movable contact.

4. In a thermostatic switch, a contact arm, a movable contact looselymounted on one side of said arm adjacent one end thereof, a pair ofstationary contacts, temperature responsive means engaging the other endof said arm for moving said arm and said movable contact between openand closed positions relative to said stationary contact, and springmeans mounted on the side of said arm opposite said movable contact andserving to continuously urge said arm and movable contact to a closedposition, said spring means being mounted in a region generally oppositethe movable contact.

References Cited in the file of this patent UNITED STATES PATENTS1,612,114 Hall Dec. 28, 1926 2,228,523 Johnson Jan. 14, 1941 2,531,025Bradley Nov. 21, 1950 2,620,416 Besag et al. Dec. 2, 1952

